uiop:if-let

(uiop:if-let ((var form)...) then [else])

Binds the variables in parallel like let, then evaluates then when every variable came out non-nil and else otherwise. The bindings are established for both branches, so else can still see them.

A single un-nested binding is accepted as well — (uiop:if-let (x form) ...) — which is how UIOP itself spells the one-variable case; a binding list whose first element is a symbol is the one binding.

uiop is ASDF's portability layer, not part of Common Lisp: the name is only reachable with the uiop: qualifier. This is UIOP's own copy of alexandria's macro of the same name, and the two behave identically.

Backend support

Works on all four backends: it is a built-in macro expansion shared by the interpreter and both compilers. Like the other built-in macros it has no function value (#'uiop:if-let is an error).